My Peonies Won't Grow

Peony buds can be killed by a late frost.

Peonies (Paeonia spp.) are large, showy perennials. The plants, which can reach maximum heights and widths of 3 feet or more, feature wide, heavily ruffled flowers in shades of red, white, yellow and pink. Peonies that fail to grow are a major disappointment, as mature peonies are a showpiece in any home garden. The failure may be due to adverse environmental conditions or diseases.

Age of the Plant

Peonies are slow growers. A peony grown from seed will not produce flowers until it is at least 5 years old, and sometimes it takes up to 7 years for a peony to bloom, according to the North Dakota State University Extension Service. For that reason, many home gardeners purchase and plant older peonies. On the other hand, plants that are too old often show reduced blooming or stop blooming entirely. This is because they get crowded. In general, peonies should be divided about every 5 years or so after they first start blooming. In these cases, dividing the plant should help, but keep in mind that newly divided peonies don't usually bloom the first year after being transplanted.

Climate and Cold

Peonies are winter-hardy in U.S. Department of Agriculture plant hardiness zones 3 through 8, and can tolerate freezing temperatures with no problem -- unless those temperatures come after the plant has produced buds. Late spring freezes can kill the buds before they open. So if it seems like your peony isn't growing because it didn't bloom, it might be that the tender buds were killed by a late spring frost. This doesn't mean your plant isn't growing -- it just means it won't be blooming this year.

Too Much Shade

Peonies need a lot of sunlight -- in fact, they pretty much need full sun, which means a total of at least 6 hours of direct sunlight, in order to grow and bloom. If they are in shade for most of the day, they won't grow or bloom very well, if at all. Another thing that stunts the growth of these plants is being planted too deeply. They should be planted so that the roots are only two inches below the surface of the soil. If you think your peony isn't growing because of where or how it's planted, dig it up and put it in a new, sunnier, shallower location.

Pests and Diseases

Most pests and diseases affect the foliage or flowers of the plant rather than stifling growth. Botrytis blight, a fungal disease, may cause the buds to fall or rot rather than open. Apply a fungicide containing fenhexamid in the spring, or even later during the growing season if you see signs of infection. Dilute the fungicide with water at a ratio of 4 ounces for every 25 gallons of water. Then, spray the plant thoroughly with the diluted mixture, protecting your skin and eyes as you apply the spray. To prevent the fungus from spreading, destroy infected buds, leaves and stems in the fall, and remove flowers as soon as they fade to prevent them from getting the disease. To help prevent Botrytis blight and other fungal diseases, water at the level of the soil, keeping the foliage as dry as possible. One disease that will cause your plant to stop growing is root rot. This is a fungal disease, caused by wet, saturated soil, that destroys the roots of the plant. The plant usually can't be saved, but you can prevent root rot by making sure your peony is planted in well-draining soil.